Affinity assay systems are commonly used in clinical and non-clinical situations to detect, monitor, or confirm the identity, amount, or presence of a particular ligand. Examples include immunoassays for the detection of an antibody or antigen, such as enzyme linked immunoassay (ELISA) or radioimmunoassay (RIA). Such affinity assays confer specificity and sensitivity to the analysis of a particular ligand in a complex sample, such as blood or other body fluid.
Conventional affinity assays employing conventional labeling and detection techniques typically require washing and/or separation steps. In addition, many affinity assay systems require detection in a machine such as a spectrophotometer or fluorimeter. These are not practical when detection of the ligand in whole blood and other light absorbing or scattering biological fluids is desired. Some conventional affinity assays, not requiring such equipment, rely on visible color changes for detection of ligand, which is also not practical in an opaque or colored fluid such as blood. Furthermore, the commonly used detection compounds, of conventional assays, such as hydrogen peroxide, arc rapidly eliminated by protective enzymes found in blood and other tissues, such as catalase.
An affinity assay providing sensitive, efficient, and rapid detection of a ligand in a complex sample medium, and particularly for detection in whole blood is needed. A preferred assay would not require washing or separation steps, sample removal to machinery for analysis, and most preferably, would utilize only materials contained or generated in its probe, materials available in the biological fluids analyzed or, if added, not rapidly decomposed by enzymes in biological fluids. An affinity assay satisfying these criteria would permit the production of affinity assay systems to detect ligands in whole blood. Such an affinity assay system is described in the instant invention.